Optical transceivers are used in optical communications systems to convert data signals from an electrical format into an optical format and vice versa. A typical optical transceiver comprises a number of separate optical, opto-electronic and electrical components, including a semiconductor laser diode (LD) or light emitting diode (LED) optical transmitting device, an electrical integrated circuit (IC) driver for providing the electrical data input to the optical transmitting device, an optical receiving device in the form of a P-I-N photodiode (PD) or avalanche photodiode (APD) and a transimpedance amplifier (TIA) for boosting the signal strength of the electrical version of the received optical signal.
The semiconductor laser is usually packaged together with a power monitoring photodiode and coupled to a lens system to form a transmitter optical subassembly (TOSA). The transmitter IC driver controls the laser operation and maintains a constant average laser output power through a feedback loop, while modulating the laser to convert electrical data signals into an optical data output signal. The feedback loop compensates for laser power changes as a result of, for example, laser aging, temperature variations, and the like.
The photodiode is usually packaged with a lens system to form a receiver optical subassembly (ROSA). The photodiode receives and converts an incoming optical data signal into electrical current, while the TIA converts the electrical current into an electrical voltage signal with linear amplification that faithfully represents the received optical data.
In most cases, it is desirable to monitor certain operational parameters of optical transceivers, such as laser bias current, laser average output power, average power (or optical modulation amplitude) as incoming at the receiver, power supply levels of the transceiver and transceiver temperature. Indeed, certain configurations of optical transceivers may require calibration or tuning of one or more of these parameters before the transceiver is able to properly be operated. Many prior art arrangements have been developed that perform this initial calibration and thereafter the “lifetime” operational monitoring of optical transceivers.
One prior art arrangement for performing calibration and monitoring is shown in FIG. 1. This arrangement utilizes a single integrated circuit in the form of a micro-controller (shown as micro-controller 1) to monitor and control all aspects of both a transmitter driver circuit 2 and a receiver TIA 3. In this prior art arrangement, an A/D converter 4 within micro-controller 1 accepts analog feedback signals from transmitter driver circuit 2 (bias, power) and receiver amplifier circuit 3 (RSSI). Analog control signals from a voltage source sensor 5A and a temperature sensor 5B formed as part of micro-controller 1 are also applied as inputs to A/D converter 4.
A/D converter 4 then creates digital versions of these monitor/control signals which are compared to digital values (and flags) stored in a diagnostic unit 6 and temperature lookup table 7. The results of the comparisons are thereafter stored in assigned locations within a memory 8 (the location assignments defined by industry standards). If any of the received digital monitor/control signal values falls outside of an acceptable range (recognized by comparison with the threshold values), this event is flagged and may also be used to trigger an adjustment of a related operating parameter of the transceiver (e.g., change the bias input to the laser, increase power of received signal via logic element 9A and D/A converter 9B output to transmitter driver 2).
While the arrangement as shown in FIG. 1 is useful, it is advisable in some instances to avoid the use of a single integrated circuit to perform all of the functions associated with optical transceiver monitoring. For example, measuring voltage supply levels and transceiver temperature readings within the micro-controller may result in inaccurate results (as compared to reading these values as co-located with the actual transmitter and receiver devices).